Electrosurgical instrument

ABSTRACT

An electrosurgical instrument is provided for the treatment of tissue in the presence of an electrically-conductive fluid medium. The instrument comprises an instrument shaft ( 10 ), a tissue treatment electrode ( 12 ) at one end of the shaft, and removal means, the instrument having an apertured portion ( 20   a ) through which matter can be aspirated by the removal means from the region surrounding the tissue treatment electrode. The removal means comprises a channel formed within the instrument shaft ( 10 ) and leading from the apertured portion ( 20   a ). The channel is provided with agitation means ( 14 ) for preventing the build-up of sublimation products within the channel.

This application is the U.S. national phase of International ApplicationNo. PCT/GB98/02094, filed Jul. 15, 1998.

This invention relates to an electrosurgical instrument for thetreatment of tissue in the presence of an electrically-conductive fluidmedium, to electrosurgical apparatus including such an instrument, andto an electrode unit for use in such an instrument. Endoscopicelectrosurgery is useful for treating tissue in cavities of the body,and is normally performed in the presence of a distension medium. Whenthe distension medium is a liquid, this is commonly referred to asunderwater electrosurgery, this term denoting electrosurgery in whichliving tissue is treated using an electrosurgical instrument with atreatment electrode or electrodes immersed in liquid at the operationsite. A gaseous medium is commonly employed when endoscopic surgery isperformed in a distensible body cavity of larger potential volume inwhich a liquid medium would be unsuitable, as is often the case inlaparoscopic or gastroenterological surgery.

Underwater surgery is commonly performed using endoscopic techniques, inwhich the endoscope itself may provide a conduit (commonly referred toas a working channel) for the passage of an electrode. Alternatively,the endoscope may be specifically adapted (as in a resectoscope) toinclude means for mounting an electrode, or the electrode may beintroduced into a body cavity via a separate access means at an anglewith respect to the endoscope—a technique commonly referred to astriangulation. These variations in technique can be subdivided bysurgical speciality, where one or other of the techniques has particularadvantages given the access route to the specific body cavity.Endoscopes with integral working channels, or those characterised asresectoscopes, are generally employed when the body cavity may beaccessed through a natural body opening—such as the cervical canal toaccess the endometrial cavity of the uterus, or the urethra to accessthe prostate gland and the bladder. Endoscopes specifically designed foruse in the endometrial cavity are referred to as hysteroscopes, andthose designed for use in the urinary tract include cystoscopes,urethroscopes and resectoscopes. The procedures of transurethalresection or vaporisation of the prostate gland are known as TURP andEVAP respectively. When there is no natural body opening through whichan endoscope may be passed, the technique of triangulation is commonlyemployed. Triangulation is commonly used during underwater endoscopicsurgery on joint cavities such as the knee and the shoulder. Theendoscope used in these procedures is commonly referred to as anarthroscope.

Electrosurgery is usually carried out using either a monopolarinstrument or a bipolar instrument. With monopolar electrosurgery, anactive electrode is used in the operating region, and a conductivereturn plate is secured to the patient's skin. With this arrangement,current passes from the active electrode through the patient's tissuesto the external return plate. Since the patient represents a significantportion of the circuit, input power levels have to be high (typically150 to 250 watts), to compensate for the resistive current limiting ofthe patient's tissues and, in the case of underwater electrosurgery,power losses due to the fluid medium which is rendered partiallyconductive by the presence of blood or other body fluids. Using highpower with a monopolar arrangement is also hazardous, due to the tissueheating that occurs at the return plate, which can cause severe skinburns. There is also the risk of capacitive coupling between theinstrument and patient tissues at the entry point into the body cavity.

With bipolar electrosurgery, a pair of electrodes (an active electrodeand a return electrode) are used together at the tissue applicationsite. This arrangement has advantages from the safety standpoint, due tothe relative proximity of the two electrodes so that radio frequencycurrents are limited to the region between the electrodes. However, thedepth of effect is directly related to the distance between the twoelectrodes; and, in applications requiring very small electrodes, theinter-electrode spacing becomes very small, thereby limiting tissueeffect and the output power. Spacing the electrodes further apart wouldoften obscure vision of the application site, and would require amodification in surgical technique to ensure direct contact of bothelectrodes with the tissue.

There are a number of variations to the basic design of the bipolarprobe. For example, U.S. Pat. No. 4,706,667 describes one of thefundamentals of the design, namely that the ratio of the contact areasof the return electrode and of the active electrode is greater than 7:1and smaller than 20:1 for cutting purposes. This range relates only tocutting electrode configurations. When a bipolar instrument is used fordesiccation or coagulation, the ratio of the contact areas of the twoelectrodes may be reduced to approximately 1:1 to avoid differentialelectrical stresses occurring at the contact between the tissue and theelectrode.

The electrical junction between the return electrode and tissue can besupported by wetting of the tissue by a conductive solution such asnormal saline. This ensures that the surgical effect is limited to theactive electrode, with the electric circuit between the two electrodesbeing completed by the tissue. One of the obvious limitations with thedesign is that the active electrode (typically a needle) must becompletely buried in the tissue to enable the return electrode tocomplete the circuit. Another problem is one of the orientation: even arelatively small change in application angle from the idealperpendicular contact with respect to the tissue surface, will changethe contact area ratio, so that a surgical effect can occur in thetissue in contact with the return electrode.

Cavity distension provides space for gaining access to the operationsite, to improve visualisation, and to allow for manipulation ofinstruments. In low volume body cavities, particularly where it isdesirable to distend the cavity under higher pressure, liquid ratherthan gas is more commonly used due to better optical characteristics,and because it washes blood away from the operative site.

Conventional underwater electrosurgery has been performed using anon-conductive liquid (such as 1.5% glycine) as an irrigant, or as adistension medium to eliminate electrical conduction losses. Glycine isused in isotonic concentrations to prevent osmotic changes in the bloodwhen intra-vascular absorption occurs. In the course of an operation,veins may be severed, with resultant infusion of the liquid into thecirculation, which could cause, among other things, a dilution of serumsodium which can lead to a condition known as water intoxication.

The applicants have found that it is possible to use a conductive liquidmedium, such as normal saline, in underwater endoscopic electrosurgeryin place of non-conductive, electrolyte-free solutions. Normal saline isthe preferred distension medium in underwater endoscopic surgery whenelectrosurgery is not contemplated, or a non-electrical tissue effectsuch as laser treatment is being used. Although normal saline (0.9% w/v;150 mmol/l) has an electrical conductivity somewhat greater than that ofmost body tissue, it has the advantage that displacement by absorptionor extravasation from the operative site produces little physiologicaleffect, and the so-called water intoxication effects of non-conductive,electrolyte-free solutions are avoided.

Carbon dioxide is the preferred gaseous distension medium, primarilybecause of its non-toxic nature and high water solubility.

The applicants have developed a bipolar instrument suitable forunderwater electrosurgery using a conductive liquid or gaseous medium.This electrosurgical instrument for the treatment of tissue in thepresence of a fluid medium, comprises an instrument body having ahandpiece and an instrument shaft and an electrode assembly, at one endof the shaft. The electrode assembly comprises a tissue treatment(active) electrode which is exposed at the extreme distal end of theinstrument, and a return electrode which is electrically insulated fromthe tissue treatment electrode and has a fluid contact surface spacedproximally from the exposed part of the tissue treatment electrode. Inuse of the instrument, the tissue treatment electrode is applied to thetissue to be treated whilst the return electrode, being spacedproximally from the exposed part of the tissue treatment electrode, isnormally spaced from the tissue and serves to complete anelectrosurgical current loop from the tissue treatment electrode throughthe tissue and the fluid medium. This electrosurgical instrument isdescribed in the specification of our International Patent ApplicationNo. PCT/GB96101473.

The electrode structure of this instrument, in combination with anelectrically-conductive fluid medium largely avoids the problemsexperienced with monopolar or bipolar electrosurgery. In particular,input power levels are much lower than those generally necessary with amonopolar arrangement (typically 100 watts). Moreover, because of therelatively large spacing between its electrodes, an improved depth ofeffect is obtained compared with conventional bipolar arrangements.

The specification of our International Patent Application No. GB96/01472describes an irrigated bipolar electrosurgical instrument that can beused in open air or gas-filled environments. This instrument includes aninternal channel for feeding electrically-conductive fluid (typicallysaline) to the exposed end of a tissue treatment electrode so as toprovide a conductive fluid path that completes an electrical circuit toa return electrode when the instrument is in use. This instrument alsoincludes an internal channel for removing fluid from the region of theexposed end of the tissue treatment electrode. When the fluid is aliquid, such as saline, the presence of that liquid can cause collateraltissue damage, so its removal is desirable. This type of instrument isintended primarily for use in open air or gas-filled environments, andis not suitable for use with electrosurgical procedures which requiredistension of a body cavity.

However, where the volume of a body cavity is small—for example inarthroscopic surgery where even the large joints, such as the knee, mayonly accommodate 50-60 ml of irrigation fluid—the following problems mayoccur, namely:

(i) Heated fluid in the immediate vicinity of the tissue contactelectrode can cause collateral tissue damage;

(ii) The products of the tissue vaporised by the tissue contactelectrode can cause visualisation problems; and

(iii) Soft tissue present in a joint space tends to move about, makingit difficult to apply the active electrode to vaporise such tissue.

An arthroscope electrode may be characterised as short (100 to 140 mm),and rigid with a working diameter up to 5 mm. It can be introducedthrough a stab incision into a joint cavity (with or without a cannula)using the triangulation technique. Such an electrode is operated with amotion which moves the electrode between the 9 O'Clock and 3 O'Clockpositions on the arthroscopic image. As a result, the tissue to betreated is usually approached at a shallow working angle with respect tothe axis of the electrode. An arthroscopic electrode thus needs to havean effect consistent with this angled approach to the tissue. The tissueto be treated, such as meniscal cartilage, is commonly dense and of ahigh electrical impedance. An arthroscope electrode requires outputpower and voltage settings that reflect the type of tissue beingtreated, the size of electrode, and the fact that arthroscopists areseeking a speed of effect comparable to that of the mechanical shaverdevices they currently employ, albeit with an electrode of smallerdimensions than a shaver blade for improved access.

The specification of our British Patent Application 9612993.7 describesan electrosurgical instrument for the treatment of tissue in thepresence of an electrically-conductive fluid medium. The instrumentcomprises an instrument shaft, and an electrode assembly at one end ofthe shaft, the electrode assembly comprising a tissue treatmentelectrode and a return electrode which is electrically insulated fromthe tissue treatment electrode by means of an insulation member. Thetissue treatment electrode has an exposed end for treating tissue, andthe return electrode has a fluid contact surface which is spaced fromthe tissue treatment electrode in such a manner as to define, in use, aconductive fluid path that completes an electrical circuit between thetissue treatment electrode and the return electrode. The electrodeassembly is provided with a plurality of apertures in the region of thetissue treatment electrode, through which apertures vapour bubblesand/or particulate material can be aspirated from the region surroundingthe tissue treatment electrode.

An RF generator is provided for powering the electrode assembly. Thepower required from the RF generator to achieve vaporisation depends ona number of variables more fully described in the specification of ourInternational Patent Application No. GB97/00065. Of these variables two,are of particular importance in the context of the present invention;one being the cooling effect produced by the aspiration of conductivefluid in the region of the tissue contact electrode, and the other beingthe disruption of the vapour pocket formed around the tissue contactelectrode by the flow of conductive fluid. These problems can bepartially overcome by coordinating the aspiration by monitoring theoutput features of the generator which indicate the vaporisation powerthreshold has been exceeded. This usually results in a series of suctionpulses as the vaporisation threshold is repeatedly exceeded betweenpulses and then elevated during the suction pulses so that, shouldvaporisation be maintained, the suction will be applied continuously. Byusing this technique, heated saline in the vicinity of the tissuecontact electrode and vaporisation products can be successfully removed.The other desirable feature is the aspiration of loose tissue towardsthe tissue contact electrode, so that it can be stabilised duringvaporisation. Whilst this can be achieved according to this technique;there are two significant performance limitations.

The first of these limitations is that the gaseous products of tissuevaporisation contain fatty products which have a sublimation property,i.e. they condense directly to a solid; sublimation occurring attemperatures well above boiling point. As the electrode shaft within thebody cavity is cooled by the surrounding saline, these products areeasily condensed. Thus, if a parallel suction shaft is used, the buildup is along its entire length, and eventually completely blocks thetube. This process, even at the flow rates dictated by minimal influenceon the power threshold, can cause very rapid blocking. For example, itis found that, with a moderately large electrode tip, using a 1 mminternal diameter suction tube, complete blockage occurs after 30seconds of activation. Obviously, a larger tube bore would increase thetime before blockage, but this occurs so rapidly that the required boresize for a useful electrode life is beyond the dimensions of the maximumshaft diameter. The problems of sublimation are compounded by aspirationof tissue pieces which are incompletely vaporised before being excisedfrom the remainder of the tissue. Given the need to attract tissue and,therefore, the requirement for a strong suction pressure which, oncetissue is engaged with the tissue contact electrode and the vaporisationthreshold is continually exceeded by cessation of flow, increases thepropensity for aspiration of unvaporised tissue and blockage of theaspiration channel.

The second of these limitations also relates to adherence of tissue tothe tissue contact electrode. As indicated above, once the tissueobstructs flow, the vaporisation power threshold is exceeded, andsuction is continuously applied. Under these circumstances, andparticularly when aspiration channels are provided adjacent to thetissue treatment electrode, a steady state can be reached wherein thetissue is held around the periphery of the tissue contact electrode, theportion of tissue in the immediate vicinity of the tissue treatmentelectrode is vaporised but, without moving the application site orredirecting suction solely through the tissue treatment electrode, nofurther removal of tissue will occur. For example, large pieces oftissue tend to bridge the tissue treatment electrode, so that all tissuein contact with the electrode is removed, but the bulk of the tissue isleft in place. Applying suction solely through the tissue treatmentelectrode limits the size of the electrode otherwise two extremes arecreated where, on the one hand during activation in conductive fluid,the vaporisation power threshold is very elevated despite synchronisingsuction pulses with the RF output, typically >200 Watts, yet, on theother hand, can be reduced to below 50% of this level once tissue isengaged. With a static tissue contact electrode, there is an inevitablecompromise between these performances variables.

The aim of the invention to provide an improved electrosurgicalinstrument of this type.

The present invention provides an electrosurgical instrument for thetreatment of tissue in the presence of an electrically-conductive fluidmedium, the instrument comprising an instrument shaft, a tissuetreatment electrode mounted at the distal end of the shaft, and removalmeans, the instrument having an apertured portion through which mattercan be aspirated by the removal means from the region surrounding thetissue treatment electrode, the removal means comprising a channelformed within the instrument shaft and leading from the aperturedportion, wherein the channel is provided with agitation means movablerelative thereto.

The agitation means thus prevents the build-up of sublimation productswithin the channel.

The instrument may further comprise drive means for moving the tissuetreatment electrode relative to the distal end of the shaft.

Advantageously, the instrument further comprises a return electrodewhich is electrically insulated from the tissue treatment electrode byinsulation means, the tissue treatment electrode being exposed at thedistal end of the instrument, and the return electrode having a fluidcontact surface spaced proximally from the exposed end of the tissuetreatment electrodes.

In a preferred embodiment, the tissue treatment electrode is movablecyclically relative to the return electrode so as to move the tissuetreatment electrode into, and out of, at least one position in whicharcing occurs between the tissue treatment and return electrode.

Preferably, the channel is defined by the instrument shaft, and theagitation means is constituted by a rod mounted within, and movablerelative to, the instrument shaft.

Conveniently, the tissue treatment electrode is constituted by thedistal end portion of the rod. Thus, movement of the rod results inmovement of the tissue treatment electrode, and this prevents tissuebridging, as the tendency for tissue to obstruct the channel is obviatedby the electrode movement ensuring that such tissue is treated. Tissuecan, therefore, be electrosurgically removed from an operation site by avaporisation technique, and can be electrosurgically morcellated (thatis to say chewed up) in this region by the moving tissue treatmentelectrode, this process being analogous to a miniature liquidiser.

Advantageously, the rod is constituted by a tungsten wire having adiameter in the range of from 0.2 mm to 1.0 mm. Preferably, the tungstenwire has a diameter in the range of from 0.4 mm to 0.6 mm.

Advantageously, the tissue treatment electrode is angled with respect tothe longitudinal axis of the instrument shaft, and the instrumentfurther comprises an insulating sleeve surrounding the rod proximally ofsaid angled end portion. The insulating sleeve may be a ceramic sleeve.

Preferably, the instrument further comprises an insulation memberprovided at the distal end of the instrument shaft, the insulationmember defining said apertured region. The insulation member may be madeof a ceramic material.

Advantageously, the insulation member is formed with a slot whichconstitutes the apertured region, the tissue treatment electrode passingthrough the slot. Alternatively, the apertured region is constituted bya gap between the tissue treatment electrode and the insulation member.

In a preferred embodiment, the drive means is such as to reciprocate therod within the channel. Advantageously, the drive means is constitutedby a motor and coupling means for convening the rotary output of themotor into reciprocatory movement of the rod.

In this case, the angled end portion of the rod may be at right-anglesto the longitudinal axis of the instrument shaft, and the tip of theangled end portion may constitute the tissue contacting portion of thetissue treatment electrode. This electrode is, therefore, a side effectelectrode.

In another preferred embodiment, the drive means is such as to rotatethe rod within the channel. An electric motor may constitute the drivemeans.

In this case, the drive rod may be formed with a portion off-set fromthe longitudinal axis of the instrument shaft.

Advantageously, the angled end portion of the rod is at right-angles tothe longitudinal axis of the instrument shaft, and the distal endsurface of said angled end portion constitutes the tissue contactingportion of the tissue treatment electrode. The rotation of the angledend portion of the rod permits the use of a small diameter rod, andhence the use of a small tissue treatment electrode, whilst providing arelatively large area tissue contacting position. The use of a smalldiameter tissue treatment electrode also permits the use of lowerelectrosurgical powers and/or higher fluid medium flow rates.

Alternatively, the angled end portion of the rod makes an acute anglewith the longitudinal axis of the instrument shaft, and the insulationmember is provided with an inclined cam surface which is engagable withthe apex of the angled end portion of the rod.

It is also possible for the angled end portion of the rod to be bentback around the distal end portion of the insulating sleeve.

Preferably, the removal means further comprises a pump connected to thechannel at a region thereof remote from the apertured portion of theinstrument. The pump may be activated cyclically whereby matter isaspirated by the removal means in a pulsed fashion. Conveniently, thepump is activated only when the tissue treatment electrode is poweredfor tissue vaporisation.

The instrument may further comprise an RF generator having a bipolaroutput connected to the tissue treatment electrode and the returnelectrode. Advantageously, the RF generator supplies energy to the drivemeans. Preferably, the pump is controlled in dependence upon the outputcharacteristics of the RF generator.

The electrosurgical instrument of the invention is useful fordissection, resection, vaporisation, desiccation and coagulation oftissue, as well as for combinations of these functions. It has aparticular application in arthroscopic surgery as it pertains toendoscopic and percutaneous procedures performed on joints of the bodyincluding, but not limited to, such techniques as they apply to thespine and other non-synovial joints. Arthroscopic operative proceduresmay include: partial or complete meniscectomy of the knee jointincluding meniscal cystectomy; lateral retinacular release of the kneejoint; removal of anterior and posterior cruciate ligaments or remnantsthereof; labral tear resection, acromioplasty, bursectomy andsubacromial decompression of the shoulder joint; anterior release of thetemperomandibular joint; synovectomy, cartilage debridement,chondroplasty, division of intra-articular adhesions, fracture andtendon debridement as applied to any of the synovial joints of the body;inducing thermal shrinkage of joint capsules as a treatment forrecurrent dislocation, subluxation or repetitive stress injury to anyarticulated joint of the body; discectomy either in the treatment of adisc prolapse or as part of a spinal fusion via a posterior or anteriorapproach to the cervical, thoracic and lumbar spine or any other fibrousjoint for similar purposes; excision of diseased tissue; andhaemostasis.

The instrument of the invention is also useful for dissection,resection, vaporisation, desiccation and coagulation of tissue, as wellas combinations of these functions, with particular application inurological endoscopic (urethroscopy, cystoscopy, ureteroscopy andnephroscopy) and percutaneous surgery. Urological procedures mayinclude: electro-vaporisation of the prostate gland (EVAP) and othervariants of the procedure commonly referred to as transurethralresection of the prostate (TURP) including, but not limited to,interstitial ablation of the prostate gland by a percutaneous orperurethral route whether performed for benign or malignant disease;transurethral or percutaneous resection of urinary tract tumours as theymay arise as primary or secondary neoplasms, and further as they mayarise anywhere in the urological tract from the calyces of the kidney tothe external urethral meatus; division of strictures as they may ariseat the pelviureteric junction (PUJ), ureter, ureteral orifice, bladderneck or urethra; correction of ureterocoele; shrinkage of bladderdiverticular; cystoplasty procedures as they pertain to corrections ofvoiding dysfunction; thermally induced shrinkage of the pelvic floor asa corrective treatment for bladder neck descent; excision of diseasedtissue; and haemostasis.

The electrosurgical instrument of the invention is also useful fordissection, resection, vaporisation, desiccation and coagulation oftissue and combinations of these functions with particular applicationin laparascopic, colposcopic (including vaginal speculum) and opensurgical procedures on the female genital tract and adnexal relateddiseases. Laparascopic operative procedures may include: removal ofsubserosal and pedunculated fibroids, ablation of ectopic endometrium,ovarian cystectomy and ovarian drilling procedures; oophorectomy,salpingo-oophorectomy, subtotal hysterectomy and laparaoscopicallyassisted vaginal hysterectomy (LAVH) as may be performed for benign ormalignant diseases; laparoscopic uterosacral nerve ablation (LUNA);fallopian tube surgery as correction of ectopic pregnancy orcomplications arising from acquired obstructions; division of abdominaladhesions; and haemostasis.

The electrosurgical instrument of the invention is also useful in thelower female genital tract, including treatment of cervix, vagina andexternal genitalia whether accessed directly or using instrumentationcomprising generally speculae and colposcopes. Such applicationsinclude: vaginal hysterectomy and other pelvic procedures utilisingvaginal access; LLETZ/LEEP procedure (large loop excision of thetransformation zone) or excision of the transformation zone of theendocervix; removal of cystic or septic lesions; ablation of genital orvenereal warts; excision of benign and malignant lesions; cosmetic andsurgical repairs including vaginal prolapse; excision of diseasedtissue; and haemostasis.

The electrosurgical instrument of the invention is also useful fordissection, resection, vaporisation, desiccation and coagulation oftissue and combinations of these functions with particular applicationin surgery on the ear, nose and throat (ENT), and more particularlyprocedures performed on the oropharynx, nasopharynx and sinuses. Theseprocedures may be performed through the mouth or nose using speculae orgags or using endoscopic techniques such as functional endoscopic sinussurgery (FESS). Functional endoscopic sinus procedures may include:removal of chronically-diseased inflamed and hypertrophic mucus linings,polyps and neoplasms from the various anatomical sinuses of the skull;excision of diseased tissue; and haemostasis. Procedures on thenasopharynx may include: removal of chronically-diseased inflamed andhypertrophic mucus linings, polyps and neoplasms from the turbinates andnasal passages; submucous resection of the nasal septum; excision ofdiseased tissue; and haemostasis. Procedures on the oropharynx mayinclude: removal of chronically-diseased, inflamed and hypertrophictissue, polyps and neoplasms particularly as they occur related to thetonsil, adenoid, epi-glottic and supra-glottic regions, and salivaryglands; as an alternative method to perform the procedure commonly knownas laser assisted uvolopalatoplasty (LAUP); excision of diseased tissue;and haemostasis.

It is evident from the scope of applications of the invention that ithas further additional applications for dissection, resection,vaporisation, desiccation and coagulation of tissue and combinations ofthese functions in general laparoscopic, thoracscopic and neurosurgicalprocedures, being particularly useful in the removal of diseased tissueand neoplastic disease whether benign or malignant.

Surgical procedures using the electrosurgical instrument of theinvention may also include introducing the electrode assembly to thesurgical site, whether through an artificial conduit (a cannula) or anatural conduit, which may be in an anatomical body cavity or space, orone created surgically. The cavity or space may be distended during theprocedure using a fluid, or may be naturally held open by anatomicalstructures. The surgical site may be bathed in a continuous flow ofconductive fluid such as saline solution either to fill and distend thecavity, or to create a locally-irrigated environment around the tip ofthe electrode assembly in a gas filled cavity. The irrigating fluid maybe aspirated from the surgical site to remove products created byapplication of the RF energy, tissue debris or blood. The procedures mayinclude simultaneous viewing of the site via an endoscope, or using anindirect visualisation means. An irrigated bipolar electrosurgicalinstrument is described in the specification of our International PatentApplication No. PCT/GB96/01472.

The invention will now be described in greater detail, by way of examplewith reference to the drawings, in which:

FIG. 1 is a diagram showing an electrosurgical apparatus constructed inaccordance with the invention;

FIG. 2 is a diagrammatic side elevation, partially broken away, of afirst form of electrode unit constructed in accordance with theinvention;

FIG. 3 is a diagrammatic side elevation of the electrode assembly of theelectrode unit of FIG. 2;

FIG. 4 is a diagrammatic side elevation, partially broken away, of asecond form of electrode unit constructed in accordance with theinvention;

FIG. 5 is a diagrammatic side elevation of the electrode assembly of theelectrode unit of FIG. 4;

FIG. 6 is a diagrammatic side elevation, partially broken away, of athird form of electrode unit constructed in accordance with theinvention;

FIG. 7 is a diagrammatic side elevation of the electrode assembly of theelectrode unit of FIG. 6;

FIG. 8 is a diagrammatic side elevation, partially broken away, of afourth form of electrode unit constructed in accordance with theinvention; and

FIG. 9 is a diagrammatic side elevation of the electrode assembly of theelectrode unit of FIG. 8.

Referring to the drawings, FIG. 1 shows electrosurgical apparatusincluding a generator 1 having an output socket 2 providing a radiofrequency (RF) output, via a connection cord 4, for an instrument in theform of a handpiece 3. Activation of the generator 1 may be performedfrom the handpiece 3 via a control connection (not shown) in the cord 4,or by means of a footswitch unit 5 connected separately to the rear ofthe generator 1 by a footswitch connection cord 6. In the illustratedembodiment, the footswitch unit 5 has two footswitches 5 a and 5 b forselecting a desiccation mode and a vaporisation mode of the generator 1respectively. The generator front panel has push buttons 7 a and 7 b forrespectively setting desiccation and vaporisation power levels, whichare indicated in a display 8. Push buttons 9 are provided as analternative means for selection between the desiccation and vaporisationmodes.

The handpiece 3 mounts a detachable electrode unit E, such as theelectrode units E1 and E4 to be described below.

FIG. 2 shows the first form of electrode unit E1 for detachablefastening to the electrosurgical instrument handpiece 3, the electrodeunit comprising a shaft 10, which is constituted by a tube made ofstainless steel. A tissue treatment (active) electrode 12 is provided atthe distal end portion of the shaft 10. The active electrode 12 isprovided by the distal end portion of a rod 14 made of tungsten, theactive electrode extending at right angles to the rod. The rod 14 has adiameter of 0.4 to 0.6 mm. A ceramic tube 18 is fixed to the rod 14immediately adjacent to the active electrode 12. A ceramic tip 20 isfixed within the out-turned distal end portion of the shaft 10.

As shown in FIG. 2, the active electrode 12 protrudes through alongitudinal slot 20 a formed in the ceramic tip 20. That portion of therod 14 not covered by the ceramic tube 18 is provided with an insulatingsleeve 22 made of polyimide, polytetrafluoroethylene or by separatesleeves made by these two substances. A heat sleeve 24 made ofpolytetrafluoroethylene or polyimide, covers the adjoining regions ofthe ceramic tube 18 and the sleeve 22.

The major portion of the length of the shaft 10 is provided with aninsulating heat shrink sleeve 26 made of polyvinylidenefluoride. Thesleeve 26 does not cover the distal end portion of the shaft 10, thatregion of the shaft constituting a return electrode 28.

The rod 14 is mounted for reciprocal movement within the shaft 10, thatend of the rod remote from the active electrode 12 being fixed to acoupling member 30 slidably mounted within one end 32 a of a sleeve 32made of stainless steel. The other end 32 b of the sleeve 32 is fixed tothe adjacent end portion of the shaft 10. A top hat washer 34 is locatedwithin the sleeve end 32 b, the washer constituting a backing member fora silicone gland 36 and a delrin bush 38. A return spring 40 actsbetween the bush 38 and the coupling member 30. The rod 14 passesthrough apertures in the washer 34, the gland 36 and the bush 38.

An off-set shaft 30 a is fixed to the end face of the coupling member30, the free end of this shaft being engageable with an inclined endface 42 a of a rotatable coupling member 42 fixed to the rotary outputshaft of a motor 44. Hence, rotation of the output shaft of the motor 44results in reciprocation of the coupling member 30 and the rod 14.

The hollow interior of the shaft 10 is connected to a transverse tubularmember 10 a which is connected to a suction pump (not shown), and soconstitutes a suction/exhaust port. As shown in FIG. 2, the activeelectrode 12 is positioned at the end of an aspiration channelconstituted by the annular cavity defined by the interior of the shaft10 and the rod 14, so that vapour bubbles and/or particulate materialwhich, in use, are formed in the region of the active electrode, can beaspirated from the region for removal via the slot 20 a, the aspirationchannel and the port 10 a.

The RF generator 1 (not shown in FIG. 2) delivers an electrosurgicalcurrent to the electrodes 12 and 28 via connectors 46 and 48 providedrespectively on the coupling member 30 and on the sleeve 32. Thegenerator 1 includes means for varying the delivered output power tosuit different electrosurgical requirements. Thus, in a first outputpower range of from about 140 volts to 200 volts, the active electrode12 is used for tissue desiccation; and, in a second output power rangeof from about 250 volts to 600 volts, the active electrode is used fortissue removal by cutting or vaporisation. For both ranges, the voltagesare peak voltages. The generator 1 may be as described in thespecification of our European Patent Application 96304558.8.

This electrosurgical instrument is particularly useful for rapid tissuedebulking and the removal of loose tissue. One of the problems whichcould be encountered when tissue is rapidly debulked using anarthoscopic electrode configuration, particularly when working in smalljoint spaces, is the production of vapour bubbles generated as an endproduct of tissue vaporisation. Such bubbles obscure vision, and cancoalesce at the site of tissue application, so that an electricalcircuit between the active and return electrodes having filamentary,mesh or coiled spring forms goes some way to solving this problem as itreduces the vaporisation threshold as disclosed in the specification ofour International patent application No. GB97100065.

The provision of the suction pump ensures the elimination of vapourbubbles from an operation site, which is particularly advantageousduring aggressive tissue debulking. The suction pump is activated onlywhen the active electrode 12 is powered for tissue vaporisation. Thepump is, therefore, pulsed so as to pull saline over the activeelectrode 12 (and to extract vapour bubbles and/or particulatematerial). This cools the active electrode 12, resulting in the collapseof the vapour pocket surrounding the active electrode. This, in turn,leads to the suction pump being turned off, thereby reducing the flow ofsaline over the active electrode 12. This electrode 12 then heats upagain, leading to the re-formation of a vapour pocket, and there-activation of the suction pump. This cycle then repeats until thegenerator 1 is turned off when the instrument is removed from theoperation site.

The suction pump must be controlled so that the flow of bubbles from theactive electrode 12 is balanced to the output characteristics of the RFgenerator 1 to prevent excessive cooling of the active electrode and aresultant increase in its vaporisation power threshold. The thermal massof the thin, wire-form active electrode 12 is lower than that of astandard solid form active electrode, and this assists in rapidlyre-established the vapour pocket around the active electrode should thiscollapse following excessive cooling.

The electrode unit E1 is intended primarily for use in arthroscopicsurgery which requires rapid tissue debulking by vaporisation. Theside-effect electrode (i.e. where the treatment axis is perpendicular tothe shaft) configuration of the unit E1 is particularly advantageous forthis purpose. In use, the electrosurgical instrument is manipulated tointroduce the electrode assembly constituted by the active electrode 12and the return electrode 28 into a selected operation site (e.g. withinthe joint space of a knee), so that the active electrode contacts thetissue to be treated, and the tissue and the electrode assembly areimmersed in saline.

The footswitch 5 b (or the push button 7 b) is then operated to activatethe generator 1. The generator 1 then provides sufficient RF power tothe electrode assembly to vaporise the saline surrounding the activeelectrode 12, and to maintain a vapour pocket surrounding thiselectrode. Using a brushing technique, with firm pressure against thetissue surface, rapid debulking of the tissue is achieved. Gentlytouching the tissue will reduce the effect, and can be used to sculptureand smooth the residual tissue surface. With tissue engagement, the flowof irrigant away from the active electrode 12 will be reduced, theamount of reduction depending on the nature of the tissue surface, theapplication pressure and the suction pressure. Speed of debulking will,therefore, depend on these variables. Once the vaporisation occurs, theproducts will include vapour bubbles, carbon particles and tissuedebris. All of these products are removed from the region of the activeelectrode 12, via the shaft 10 and the port 10 a, by the suction pump.

All the constituents removed from the active tip are at hightemperatures. This could lead to a potentially dangerous heating of theelectrode shaft 10, which could cause tissue damage at the entry point.It may be, therefore, necessary to aspirate additional coolant salinefrom the body cavity along the inside surface of the shaft. To ensurethat this saline is indeed at a safe temperature, it is taken from therear of the return electrode 28 via a mesh filter (not shown).

In use, when the generator 1 is turned on, the motor 44 begins torotate, causing the rod 14 to oscillate with an amplitude of 0.5 mm. Theoscillation of the rod 14 within the shaft 10 provides a mechanicalagitation within the shaft that is sufficient to dislodge anysublimation products which condense within the shaft. In this way,blockage of the shaft 10 is prevented, so that the instrument can beused on a continuous basis.

The oscillation of the active electrode 12 also ensures that tissuepieces removed electrosurgically by vaporisation from an operation sideare morcellated electrosurgically by the oscillating electrode, therebypreventing large tissue pieces bridging the aspiration channel.Morcellation is the division of a tissue piece into many smaller piecesin order to facilitate its surgical removal.

The electrode unit E1 is also very effective in removing heated saline(distension fluid) from within a joint cavity. The risk of hotdistension fluid occurs primarily during power application to reach thevaporisation threshold. Once the threshold has been reached, the powerrequirement falls by 30-50%.

Whilst aspiration from the region of the active electrode 12 will removeheated saline from the body cavity, and remove any risk of overheatingthrough prolonged activation under conditions where the vaporisationthreshold is not reached, the cooling effect and disruption of vapourpockets created around the active electrode will increase thevaporisation threshold. A vicious cycle can, therefore, be created,wherein the more suction applied at the active electrode 12, the morepower required to reach the vaporisation threshold, and the greater therisk of heating. The other factor influencing the vaporisation thresholdis the ratio of return: active contact area, and the insulationseparation between the active electrode 12 and the return electrode 28.The size of the active electrode 12 and the insulation separation, must,therefore, be reduced to the minimum necessary to achieve the functionin order to offset the effects of aspiration in elevating the powerthreshold of vaporisation.

The specification of our International Patent Application GB97100065discloses techniques for controlling the vaporisation threshold byemploying active electrode designs which assist in capturing vapourpockets and preventing cooling of the active electrode application siteby screening from the flow of irrigant provided by channels in anendoscope. An alternative method of reducing the vaporisation powerthreshold is to pulse the suction pressure, thereby allowing thethreshold to be attained between pulses. Such pulses may be synchronisedwith the output features of the RF generator 1 to provide power burstsduring active suction to sustain the vapour pocket, and clear any tissueoccluding the apertures in the active electrode 12.

A known technique in arthroscopic surgery is to apply suction through amechanical, tissue-nibbling device so that soft tissue present in thejoint space, such as the infrapatellar fat pad, can be held in positionwithin the nibbler jaws by suction whilst it is progressively “nibbledaway”.

Attracting tissue to the active electrode 12 of the electrode unit E1has a similar effect as, for the reasons already given above, complianttissue adhering to the active electrode will result in a reduction ofthe vaporisation power threshold. Adherent tissue will be rapidlyvaporised, and small tissue particles produced during vaporisation willbe aspirated from the application site.

Because of its speed of debulking and side-effect configuration, theelectrode unit E1 also has advantages in urological surgery as an EVAPtechnique for use in conjunction with a resectoscope. A resectoscopeelectrode unit is introduced very differently, in that is mounted on anendoscope prior to passage of the assembled instrument through a workingsheath via the urethra. The proximal end of the electrode unit isconnected to a trigger assembly and an electrical contact which isintegral with the resectoscope. By this means, the electrode unit E1 canbe moved back and forth through a defined range of motion by operatingthe trigger mechanism. As the electrode unit E1 is assembled prior tointroduction, the size of the tip is not constrained by working channeldimensions, but rather by the diameter of the working sheath which canbe up to 10 mm. Part of this diameter is occupied by the support wiresto the electrode unit E1, which wires are commonly bent in a downwardangle, with respect to the endoscopic image, to the working tip, so thatthey do not interfere with either visulation or its operation. Becauseof the reciprocatory movement of the rod 14, the active electrode 12operates over a length lying within the range of from 3 mm to 4 mm and awidth lying in the range of from 2 mm to 3 mm, and this size isnecessary for urological surgery given that, on average, 20-30 grammesof prostate tissue must be removed.

Because of the reservoir effect of the urinary bladder, and the mountingof the endoscope to view the tip of the active electrode 12 from below,bubble generation during vaporisation is less of a problem duringendoscopic urology, as the bubbles flow away from the endoscope toaccumulate in the bladder. Nevertheless, the use of the electrode unitE1 substantially reduces the possibility of bubble generation causingproblems.

Although the electrode unit E1 is intended primarily for use in thevaporisation of tissue it can also be used for desiccation, particularlyof synovial membranes or to separate muscle attachments. In this case,once the electrode assembly of the electrode unit E1 has been introducedinto a selected operation site, the RF generator 1 is actuated using thefootswitch 5 a or the push button 7 a. The generator 1 will then providesufficient RF power to the electrode assembly to maintain the salineadjacent to the active electrode 12 substantially at its boiling pointwithout creating a vapour pocket surrounding that electrode. Theinstrument can then be manipulated by moving the active electrode 12across the surface of the tissue to be treated in a side-to-side“painting” technique.

The electrode unit E1 can also be used for delivering a blended poweroutput. This is achieved by automatically alternating the output of theRF generator 1 between the desiccation and vaporisation power levels,more haemostasis being produced then is possible in the vaporisationmode. As a consequence, the speed of tissue debulking is reduced, butthe increased haemostasis is useful when cutting or debulking vasculartissue structures. Alternatively, the output of the RF generator 1 canbe pulsed at the vaporisation power level, without cycled activation ofthe desiccation mode. This produces a less aggressive tissuevaporisation than occurs in the vaporisation mode, with a consequentreduction in both bubble formation and the risk of tissue charring.

The active electrode 12 of the unit E1 is a side effect electrode (i.e.its treatment axis is perpendicular to the shaft). Axial agitation isadvantageous with such electrodes, in that the entire electrode can bebrought into contact with tissue. As a result, the exposed area can bemade very small, allowing operation at lower powers and less at highersaline flow rates.

FIGS. 4 and 5 show the second form of electrode unit E2. This instrumentis a modification of that shown in FIGS. 2 and 3, and so like referencenumerals will be used for like parts, and only the modifications will bedescribed in detail. There are two main modifications, the first beingto the drive to the rod 14, and the second to the configuration of theactive electrode 12.

In the first modification, the motor 44 rotatably drives the rod 14 viaa coupling. assembly 42. As with the embodiment of FIGS. 2 and 3, therod 14 passes through aligned apertures in the washer 34, the gland 36and the delrin bush 38. The bush 38 is somewhat longer than theequivalent bush of the embodiment of FIGS. 2 and 3 extending to the end32 a of the sleeve 32. A slip ring 46a is provided to connect theconnector 46 to the rod 14.

The other main modification is that the active electrode 12 (the freeend of the tungsten rod 14—in this embodiment of 0.5 mm diameter) isbent back over the free end of the ceramic tube 18. The turned-backportion 12 a of the electrode 12 constitutes a side effect electrode. Anapertured region 20 a is formed between the ceramic tip 20 and theactive electrode 12, this region loading to the aspiration channeldefined by the interior of the shaft 10.

Another modification is that the rod 14 is a flexible drive rod whosedistal end portion is off-set with respect to the central longitudinalaxis of the shaft 10. In use, when the generator 1 is turned on, themotor 44 begins to rotate, causing the rod 14 to rotate within the shaft10 This rotation provides a mechanical agitation that is sufficient todislodge any sublimation products which condense within the shaft. Theoff-set of the rod 14 results in an unstable oscillation being set up inthe rod, which sweeps adherent tissue debris from the inner wall of theshaft 10.

FIGS. 6 and 7 show the third form of electrode unit E3. This unit E3 isa modification of the unit E2, so like reference numerals will be usedfor like parts, and only the modifications will be described in detail.The main modification is to the configuration of the active electrodeassembly. Thus, as shown in FIG. 7, the active electrode 12 is shapedlike a crank handle, and defines an elbow 12 b which is off-set from theaxis of the ceramic tube 18. The ceramic tip 20 is formed with aninclined cam surface 20 b which, in use, engages with the elbow 12 b toforce the tip of the active electrode 12 outwardly, and to ensure bettertissue engagement. This crank handle configuration of the activeelectrode 12 also ensures that, as the tip rotates, the elbow 12 b ispushed around the inner surface of the ceramic tip 20, thereby removingdebris which would otherwise tend to build up there.

FIGS. 8 and 9 show the fourth form of electrode unit F4. This unit E4 isalso a modification of the unit E2, so like reference numerals will beused for like parts, and only the modifications will be described indetail. Here, the main modification is to the configuration of theactive electrode 12 which, in this case, is an end effect electrode,being constituted by a simple hook-shaped end portion 12 a at the end ofthe rod 14.

As with the embodiments of FIGS. 4 and 5, the rod 14 is a flexible driverod whose distal end portion off-set with respect to the centrallongitudinal axis of the shaft 10.

As has already been described, the adherence of tissue over the activeelectrode 12 may induce a steady state condition, and the aspirationmethod must allow for removal of unvaporised tissue particles whilst notquenching vapour pocket formation. Rotation of the active electrode 12of the electrode units E2 to E4 provides several advantages to overcomethese performance issues. Thus, rotating the active electrode 12increases the effective size of the electrode, as far as tissue contactarea is concerned, for one complete rotation, whilst reducing thephysical size of the active electrode. Reducing the size of the activeelectrode 12 reduces the vaporisation power threshold to a degreesufficient to enable aspiration along the axis of rotation when thegenerator control method is employed.

The introduction of rotation and aspiration through the active electrode12, or more accurately through a channel within the range of motion ofthe active electrode, prevents the steady state being reached, and soprevents tissue bridging. This is achieved as tissue temporarilyobstructing the aspiration channel is always treated, as opposed topositioning aspiration channels outside the range of motion of theactive electrode 12, in which case only tissue adjacent to thatobstructing the aspiration channel would be treated.

Given that the aspiration channel is required to cope with unvaporisedtissue, the active electrode 12 is only required to incise the tissuesuch that the tip of the tissue in the aspiration channel is detachedfrom the body of the tissue and then aspirated through the channel.Ideally, the truncated portion of tissue is also morcellated orpartially vaporised by the active electrode 12 to reduce the size oftissue pieces. This morcellation is accomplished by introducing anoff-set in the drive shaft/connector to the active electrode 12 whichrotates in the aspiration channel of larger internal diameter than theexternal diameter of the connector, a feature which has additionaladvantages in preventing blocking of the aspiration channel, as isdescribed below.

The relative contributions of tissue incision or morcellation and tissuevaporisation to the overall tissue debulking process can be controlledby the interaction of the bore of the terminal aspiration channel, thesuction pressure and the bulk of the active electrode 12. Owing to theoverall size constraints on the external diameter of the instrument itis, in general, the diameter of the drive rod 14 whose distal tip formsthe active electrode 12 and which, therefore, also provides the means ofelectrical connection to the active electrode, which determines whethertissue removal occurs primarily by incision/morcellation orvaporisation. Typically a drive rod 14 (and hence active electrode 12)formed from 0.2-1.0 mm diameter tungsten wire providesincision/morcellation, and a drive rod active electrode formed from 0.5mm diameter tungsten wire primarily provides vaporisation. Theincision/morcellation technique has advantages when dealing with softfriable tissue, whereas the vaporisation technique has advantages whenapplication is made to dense fibrous or cartilaginous tissue. The designcan, therefore, be optimised for the type of tissue encountered duringuse in particular surgical specialities or, alternatively, a multifunctional design with a drive rod and active electrode typically formedfrom 0.4-0.6 mm tungsten can be used.

For all four electrode units E1 to E4, agitation within the aspirationshaft 10 significantly reduces the risk of blockage, either bymorcellated tissue, sublimated products of vaporisation or both. Thiscan be accomplished by axial or rotary motion of the rod 14 which ispositioned within the aspiration channel, with or without other means offluid agitation, including the cycling of suction pressure, which may beprovided as an integral feature of generator output, control of suction,and sonic pressure waves. To enhance the effect of agitation, it isbeneficial to construct the drive rod 14 from a lubricious material toreduce adherence.

Each of the electrode units E1 and E4, has the additional advantage thatthe aspiration in the region of the active electrode 12 restricts theflow of convection currents in the saline surrounding the electrodeassembly. As the power threshold required to reach vaporisation isdependent on the power dissipation of the active electrode 12 and theflow characteristics around it, the power threshold is dependent uponthe maximum rate of convection. Consequently, the restriction of theconvection currents reduces the power threshold and/or permits the useof higher saline flow rates, and this is advantageous as it enables theuse of a cheaper RF generator, as well as avoiding problems such asdissipation within the instrument, and catastrophic overheating of theactive electrode. It also facilitates control of the generator oncevaporisation commences. The importance of power threshold ofvaporisation is discussed in greater detail in the specification of ourInternational Patent Application No. GB97/00065.

Moreover, each of the electrode units E1 to E4 is such as to preventtissue bridging, as the tendency for tissue to obstruct the aspirationchannel is, in each case, obviated by the movement of the activeelectrode ensuring that such tissue is treated. The movement of theactive electrode 12 also ensures tissue morcellation, though this iseffected by electrosurgery rather than by mechanical cutting.

It is a feature of each of the electrode units E1 to E4 that pieces ofmorcellated tissue separated from a surgical site will be drawn into theaspiration channel by the suction pressure. Should such pieces be toolarge to enter the aspiration channel, they will be reduced in size by acombination of the mechanical action of the agitated electrode 12 andthe electrosurgical action created by the positioning of the returnelectrode 28 in relation to the aspiration channel. In the limit, thespacing of the return electrode 28 relative to the motion of theagitated electrode 12 can be adjusted to allow a controlled level ofperiodic arcing between the two. This aspect permits control of therelative strength of the mechanical and electrosurgical actions in keepthe aspiration channel clear. This aspect is described in greater detailin the specification of our British Patent Application

It will be apparent that modifications could be made to the electrodeunits described above. For example, instead of providing an off-setdrive rod 14, this rod could be loosely coiled so that the coils lieagainst the inner wall of the aspiration channel, whereby, duringrotation, a worm screw action occurs to encourage proximal movement oftissue debris, as well as cleaning of the inner wall of the channel.

The motor 44 of each of the embodiments would be powered by the RFgenerator 1. This has the advantage that the motor 44 can be controlledby means that require the RF output voltage to exceed the vaporisationpower threshold before sufficient power is delivered to energise themotor. Control means for the purpose could be mounted with the motor 44within the handpiece 3.

It would also be possible to introduce axial motion during rotation.Thus, for the electrode unit E4, the simple 90° hook form activeelectrode 12 can rotate on a bearing surface provided by the distal endface of the ceramic tube 18, this end face being provided with ratchetteeth features. Thus, as the rod 14 rotates, the hook-shaped end portion12 a moves in and out as it engages and disengages the ratchet teeth,this axial movement being permitted by the off-set flexible drive rod 14repeatedly elongating and shortening.

As an alternative to an electric motor, each of the units E1 to E4 couldbe powered by a fluid drive generated through a rotary vane or similarapparatus, which, in turn, may be powered by the suction means.

It is also possible to power the rotary drive by the RF generator 1, sothat an integral and interactive system of the rotary drive, the activeelectrode 12, the RF generator and the suction means is provided.

The upper limit of the speed of rotation of the units E2 to E4 isdefined at that level which elevates the vaporisation power thresholdbeyond the output range of the RF generator 1, which will, in turn, bedependent upon the geometry of the active electrode 12. Typically, thespeed of tissue removal is increased with increased rotary speed whenprimarily employing the incision/morcellation technique, and isincreased with decreased rotary speed when primarily employing thevaporisation technique. It is, therefore, evident that, in amulti-functional design, it is advantageous for the user to vary therotary speed depending on the nature of the tissue being treated. Tothis end, a typical range of rotary speeds would be from 100 revs/min to1000 revs/min.

With the rotary action electrode units E2 to E4, the effective size ofthe active electrode 12 is increased, and a significant aspect is theincision of tissue. The active electrode 12 is fabricated from thedistal end of the drive rod 14, so simple wire form electrodes meetthese performance requirements. The only drawback of these simpleelectrode forms is that asymmetry of the tissue contact can make itdifficult to maintain an accurate location on a tissue surface,particularly when that surface is comprised of more fibrous or moredense tissue.

If the wire form active electrode 12 protrudes from the ceramic tube 18,for example in a simple loop form as with the electrode unit E2, thenthe potential exists for the loop to excise tissue pieces too large foraspiration through the distal opening of the aspiration channel. Shouldthis occur, the exposed distal end of the drive rod 14 within theaspiration channel performs an important function in morcellating andvaporising such tissue pieces, so that they are reduced in sizesufficiently to enter the aspiration channel. This function is enhancedby the eccentric motion of the drive rod 14 within the aspirationchannel.

Whilst the amount of protrusion of the active electrode 12 from thedistal end of the ceramic tube 18 is governed by the rules described inour International Patent Application GB96/01473, the effect ofaspiration in increasing vaporisation threshold changes these rules. Theother performance factor governing the dimension of the active electrode12 is similar to that defining the diameter of the wire. Thus, thethinner wire forms, which are used on soft tissue, can protrude from thedistal end of the ceramic tube 18 in the treatment axis; whilst thethicker wire forms, which are used on more dense tissue, ideally extendbeyond the distal end of the ceramic tube in the treatment axis by anamount not exceeding the diameter of the wire.

The active electrode 12 may also take on more convoluted or more complexgenerally planar forms of end effect electrodes and generally axialforms for side effect electrodes, for example coils, spirals, meshes ormultiple spokes.

Our International Patent Application GB96/01472 describes a technique ofintroducing a conductive fluid to the region of a tissue treatment(active) electrode in order to define, in use, a conductive fluid pathbetween the active electrode and a return electrode. The electrode unitsE1 to E4 of the present invention could be modified to incorporate thosefeatures. In particular, these units could be modified for use ingaseous operating environments, either on the surface of a body orwithin body cavities.

The specification of our British Patent Application 9612993.7 describesa technique of aspiration in the vicinity of a tissue treatment (active)electrode, wherein the suction pressure is controlled by generatoroutput features in order to facilitate vaporisation by intermittentlylowering the vaporisation threshold by cessation of suction flow. Thetechniques could advantageously be incorporated in the electrode unitsE1 to E4, both to ensure the vaporisation threshold is exceeded betweensuction pulses, and as a result of the suction pulsing assisting inpreventing blockage of the aspiration channel.

As a suction pulse is initiated only once the vaporisation threshold hasbeen exceeded, tissue can only be attracted to the active electrode oncethe threshold is exceeded by activation remote from the tissue withinthe surrounding distension medium. It is known that the vaporisationthreshold is lowered once tissue is engaged by the active electrode. Itis, therefore, advantageous for suction to be applied initially withoutRF activation as a variable time delay feature.

In summary the electrosurgical instrument of the invention has thefollowing advantageous features:30

1. A small active electrode surface which is able to treat large tissueareas by virtue of active electrode movement.

2. A small active electrode to enable vaporisation, despite the coolingeffects created by aspiration.

3. A mechanical movement at the active electrode tip, compatible withmaterial removal within the aspiration channel.

4. Aspiration operation is dependent upon the vaporisation condition.

5. At least the outside of the shaft 10 is coated with a non-stickmaterial such as polytetrafluoroethylene—ideally the inside of the shaftas well.

6. Active electrode tip movement occurs across the face of theaspiration channel, so that any lodged tissue is electrosurgicallymorcellated.

7. Active electrode agitation is dependent upon the vaporisationcondition.

8. Discontinuities within the agitator rod ensure that the internalsurfaces of the shaft are cleaned; or the rod flexes sufficiently tocreate the same effect.

9. A ceramic-to-ceramic interface at the active electrode tip ensuresthat the internal circumference of the outer ceramic is wiped by theinner ceramic.

10. The agitator rod is independently insulated in ceramic at its tip.

11. Offset rotary action for a side-effect electrode to enable flatsurface engagement.

What is claimed is:
 1. An electrosurgical instrument for the treatmentof tissue in the presence of an electrically-conductive fluid medium,the instrument comprising: an instrument shaft, a tissue treatmentelectrode mounted at the distal end of the shaft, removal meanscomprising a channel formed within the instrument shaft, and anapertured portion through which matter can be aspirated by the removalmeans from the region surrounding the tissue treatment electrode, theremoval means extending from the apertured portion, wherein the channelis provided with agitation means movable relative thereto, the agitationmeans being a rod mounted within and movable relative to the instrumentshaft, the rod being rotatable within the channel and formed with aportion off-set from the longitudinal axis of the instrument shaft,whereby the off-set portion rotates within the channel around thelongitudinal axis of the instrument shaft when the rod is rotated withinthe channel.
 2. An electrosurgical instrument as claimed in claim 1,further comprising drive means for moving the tissue treatment electroderelative to the distal end of the shaft.
 3. An electrosurgicalinstrument as claimed in claim 1, further comprising a return electrodewhich is electrically insulated from the tissue treatment electrode byinsulation means, the tissue treatment electrode being exposed at thedistal end of the instrument, and the return electrode having a fluidcontact surface spaced proximally from the exposed end of the tissuetreatment electrode.
 4. An electrosurgical instrument as claimed inclaim 3, wherein the tissue treatment electrode is movable cyclicallyrelative to the return electrode so as to move the tissue treatmentelectrode into, and out of, at least one position in which arcing occursbetween the tissue treatment and return electrode.
 5. An electrosurgicalinstrument as claimed in claim 3, wherein the agitation means isconstituted by a rod mounted within, and movable relative to, theinstrument shaft.
 6. An electrosurgical instrument as claimed in claim5, wherein the tissue treatment electrode is constituted by the distalend portion of the rod.
 7. An electrosurgical instrument as claimed inclaim 6, wherein the rod is constituted by a tungsten wire having adiameter in the range of from 0.2 mm to 1.0 mm.
 8. An electrosurgicalinstrument as claimed in claim 7, wherein the tungsten wire has adiameter in the range of from 0.4 mm to 0.6 mm.
 9. An electrosurgicalinstrument as claimed in claim 6, wherein the tissue treatment electrodeis angled with respect to the longitudinal axis of the instrument shaft.10. An electrosurgical instrument as claimed in claim 9, furthercomprising an insulating sleeve surrounding the rod proximally of saidangled end portion.
 11. An electrosurgical instrument as claimed inclaim 10, wherein the insulating sleeve is a ceramic sleeve.
 12. Anelectrosurgical instrument as claimed in claim 9, wherein the angled endportion of the rod is at right-angles to the longitudinal axis of theinstrument shaft, and the tip of the angled end portion constitutes thetissue contacting portion of the tissue treatment electrode.
 13. Anelectrosurgical instrument as claimed in claim 6, wherein the insulationmeans comprises an insulation member provided at the distal end of theinstrument shaft, the insulation member defining said apertured portion.14. An electrosurgical instrument as claimed in claim 13, wherein theinsulation member is formed with a slot which constitutes the aperturedregion, the tissue treatment electrode passing through the slot.
 15. Anelectrosurgical instrument as claimed in claim 13, wherein the aperturedportion is constituted by a gap between the tissue treatment electrodeand the insulation member.
 16. An electrosurgical instrument as claimedin claim 6 further comprising drive means for moving the tissuetreatment electrode relative to the distal end of the shaft, and whereinthe drive means is such as to reciprocate the rod within the channel.17. An electrosurgical instrument as claimed in claim 16, wherein thedrive means is constituted by a motor and coupling means for convertingthe rotary output of the motor into reciprocatory movement of the rod.18. An electrosurgical instrument as claimed in claim 6 furthercomprising drive means for moving the tissue treatment electroderelative to the distal end of the shaft, and wherein the drive means issuch as to rotate the rod within the channel.
 19. An electrosurgicalinstrument as claimed in claim 18, wherein an electric motor constitutesthe drive means.
 20. An electrosurgical instrument as claimed in claim18, wherein the rod is formed with a portion off-set from thelongitudinal axis of the instrument shaft.
 21. An electrosurgicalinstrument as claimed in claim 18, wherein the angled end portion of therod is at right-angles to the longitudinal axis of the instrument shaft,and the distal end surface of said angled end portion constitutes thetissue contacting portion of the tissue treatment electrode.
 22. Anelectrosurgical instrument as claimed in claim 18, wherein the angledend portion of the rod makes an acute angle with the longitudinal axisof the instrument shaft.
 23. An electrosurgical instrument as claimed inclaim 18, wherein the angled end portion of the rod is bent back aroundthe distal end portion of the insulating sleeve.
 24. An electrosurgicalinstrument as claimed in claim 8, further comprising an RF generatorhaving a bipolar output connected to the tissue treatment electrode andthe return electrode.
 25. An electrosurgical instrument as claimed inclaim 24, wherein the pump is controlled in dependence upon the outputcharacteristics of the RF generator.
 26. An electrosurgical instrumentas claimed in claim 1, wherein the channel is defined by the instrumentshaft.
 27. An electrosurgical instrument as claimed in claim 1, whereinthe removal means further comprises a pump connected to the channel at aregion thereof remote from the apertured portion of the instrument. 28.An electrosurgical instrument as claimed in claim 27, wherein the pumpis activated cyclically whereby matter is aspirated by the removal meansin a pulsed fashion.
 29. An electrosurgical instrument as claimed inclaim 28, wherein the pump is activated only when the tissue treatmentelectrode is powered for tissue vaporisation.
 30. An electrosurgicalinstrument for the treatment of tissue in the presence of anelectrically-conductive fluid medium, the instrument comprising: aninstrument shaft, a tissue treatment electrode mounted at the distal endof the shaft, a return electrode electrically insulated from the tissuetreatment electrode by an insulation member, removal means, and drivemeans for moving the tissue treatment electrode relative to the distalend of the shaft, the instrument having an apertured portion throughwhich matter can be aspirated by the removal means from the regionsurrounding the tissue treatment electrode, the removal means comprisinga channel formed within the instrument shaft and leading from theapertured portion, the channel being provided with agitation meansmovable relative thereto, the agitation means being constituted by a rodmounted within, and movable relative to, the instrument shaft, the rodincluding an end portion angled with respect to the instrument's shaft'slongitudinal axis, the tissue treatment electrode being constituted bythe distal end portion of the rod, the drive means rotating the rodwithin the channel, wherein the angled portion of the rod makes an acuteangle with the longitudinal axis of the instrument shaft, and whereinthe insulation member is provided with an inclined cam surface which isengagable with the apex of the angled end portion of the rod.
 31. Anelectrosurgical instrument for the treatment of tissue in the presenceof an electrically-conductive fluid medium, the instrument comprising:an instrument shaft, a tissue treatment electrode mounted at the distalend of the shaft and being exposed at the distal end of the instrument,removal means, an apertured portion through which matter can beaspirated by the removal means from the region surrounding the tissuetreatment electrode, the removal means comprising a channel formedwithin the instrument shaft and leading from the apertured portion, thechannel being provided with agitation means therein and movable relativethereto, the agitation means being a rod having a portion off-set fromthe longitudinal axis of the shaft, the rod and off-set portion beingrotatable within the channel, drive means for moving the agitationmeans, whereby the tissue treatment electrode is moved relative to thedistal end of the shaft, and a return electrode which is electricallyinsulated from the tissue treatment electrode by insulation means andhaving a fluid contact surface spaced proximally from the exposed end ofthe tissue treatment electrode, an RF generator having a bipolar outputconnected to the tissue treatment electrode and the return electrode,wherein the RF generator supplies energy to the drive means.